Cleaning agent and method for cleaning ultrafiltration membranes in electrophoretic dip coating installations

ABSTRACT

Aqueous cleaning agent and its use in a process for cleaning ultrafiltration membranes in ultrafiltration units of electro-dipcoating plants, which cleaning agent contains electro-dipcoating lacquer (EDL) binders overneutalized with neutralizing agent.

BACKGROUND OF THE INVENTION

The invention relates to cleaning agents for ultrafiltration membranesin ultrafiltration units of electro-dipcoating plants. The inventionrelates also to a process for cleaning ultrafiltration membranes usingthe cleaning agents.

Electro-dipcoating (EDC) is widely used in industrial lacquering both asanodic dipcoating (ADC) and, especially, as cathodic dipcoating (CDC).In particular, it is used, for example, as CDC in the automotiveindustry for applying the anticorrosive primer coating layer to motorvehicle bodies. The EDC baths are coupled with an ultrafiltration unithaving one or more ultrafiltration modules, in which unit theelectro-dipcoating lacquer (EDL) is subjected to membrane pressurefiltration at, for example, from 1 to 5 bar (initial pressure at theultrafiltration module). During the ultrafiltration, the EDC coatingcomposition is separated at a semi-permeable membrane into aconcentrate, which is fed back into the EDC bath, and an EDLultrafiltrate (permeate). The EDL ultrafiltrate has only a low solidscontent of, for example, from greater than 0 to less than 0.5 wt. %. Itconsists mainly of water, and it contains to a subordinate degreeconstituents of the electro-dipcoating lacquer that pass through themembrane, such as neutralising agents, dissolved salts, organic solventsand low molecular weight binder constituents. The EDL ultrafiltrationhas two functions. On the one hand, the EDL ultrafiltrate that isobtained is used to rinse non-adhering EDC lacquer from the EDL-coatedsubstrates after they emerge from the EDL coating bath. After rinsing,the EDL-coated substrates are conveyed to the stoving furnace of the EDCplant. The EDL rinsed off with the EDL ultrafiltrate is fed back to theEDC bath again. The second function of the EDL ultrafiltration is thatof keeping the composition of the EDC bath constant within a certaintolerance, which is achieved by the discarding of a portion of the EDLultrafiltrate that is not used as rinsing agent. In that manner, it ispossible to prevent disruptive constituents that pass through themembrane from building up in the EDC bath.

The separating membranes within the ultrafiltration modules of EDLultrafiltration units require cleaning at intervals and, generally, alsoconditioning (impregnation) before being used for their intendedpurpose. U.S. Pat. No. 4,136,025, for example, describes a process forcleaning membranes within CDL ultrafiltration units using an aqueoussolution of an acid containing a water-soluble organic solvent. Theexample mentioned in U.S. Pat. No. 4,136,025 gives the following as thecomposition of the aqueous cleaner solution:

-   -   7.5 wt. % butyl glycol,    -   5.7 wt. % 88% aqueous lactic acid, and    -   86.8 wt. % deionised water.

The cleaning action of such cleaning agents of the prior art consistingessentially of neutralising agent, water and organic solvent is in needof improvement. For example, it has been found that, following membranecleaning using cleaning agents having such a composition, theperformance of the EDL ultrafiltration units declines ever more rapidlyfrom cleaning interval to cleaning interval in the sense of anexponential function, that is to say the cleaning intervals becomeshorter from one cleaning operation to the next until cleaning is nolonger worthwhile and the membrane or the ultrafiltration modulescontaining the membrane have to be replaced. In addition, theperformance of the EDL ultrafiltration units becomes poorer and poorerfrom cleaning interval to cleaning interval as compared with theperformance following each preceding cleaning operation. Suchdisadvantages of the use of cleaning agents of the prior art areparticularly pronounced in connection with the cleaning of modem EDLultrafiltration modules of compact construction.

The object of the invention is to provide cleaning agents that are moreeffective as compared with the prior art, and processes for cleaning EDLultrafiltration membranes.

The object can be achieved if aqueous cleaning agents containing EDLbinders overneutralised with neutralising agent are used for thecleaning of EDL ultrafiltration membranes, for example ultrafiltrationmembranes contained in EDL ultrafiltration modules of EDLultrafiltration units.

SUMMARY OF THE INVENTION

The invention provides aqueous cleaning agents that can be used for thecleaning of EDL ultrafiltration membranes and that contain EDL bindersoverneutralised with neutralising agent. The aqueous cleaning agents maybe either aqueous cleaning agents that can be used for the cleaning ofADL ultrafiltration membranes, which agents contain ADL bindersoverneutralised with base, or they are aqueous cleaning agents that canbe used for the cleaning of CDL ultrafiltration membranes and thatcontain CDL binders overneutralised with acid.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows curves showing the fall in the ultrafiltration performancewith time of the CDL ultrafiltration module cleaned according toExamples 3, 4 and 5.

DETAILED DESCRIPTION OF THE INVENTION

It is fundamental to the invention that the cleaning agents according tothe invention contain, in addition to water, EDL binders, for examplecorresponding to a solids content of from 5 to 35 wt. %. The content ofEDL binders in the cleaning agents according to the invention ispreferably from 10 to 30 wt. %, particularly preferably from 15 to 28wt. %.

The ADL binders contained in the cleaning agents according to theinvention for the cleaning of ADL ultrafiltration membranes areconventional ADL binders carrying anionic groups or groups that can beconverted into anionic groups, for example COOH, SO₃H and/or PO₃H₂groups. COOH groups are preferred. The acid numbers of such resins are,for example, from 35 to 300 mg KOH/g. The weight-average molar mass (Mw)of the resins is preferably from 300 to 10,000. Examples of ADL bindersare polyesters, epoxy resin esters, (meth)acrylic copolymer resins,maleate oils or polybutadiene oils. The ADL binders can beself-crossliiking or can be used in admixture with known cross liningagents. Examples of such crosslinking agents are aminoplastic resins,for example based on triazine, crosslinking agents containingtransesterifiable groups, or blocked polyisocyanates.

The CDL binders contained in the cleaning agents according to theinvention for the cleaning of CDL ultrafiltration membranes areconventional CDL binders containing cationic groups or basic groups thatcan be converted into cationic groups, for example amino, ammonium, e.g.quaternary ammonium, phosphonium and/or sulfonium groups. Preference isgiven to CDL binders having basic groups, particularly preferably havingnitrogen-containing basic groups, such as amino groups. Such basicresins are, for example, resins containing primary, secondary and/ortertiary amino groups. Some or all of the tertiary amino groups may bepresent in quaternised form. The amine numbers of such resins are, forexample, from 20 to 250 mg KOH/g. The weight-average molar mass (Mw) ofthe resins is preferably from 300 to 10,000. Examples of CDL binders areamino(meth)acrylate resins, aminopolyurethane resins, polybutadieneresins containing amino groups, aminoepoxy resins, and also epoxyresin-carbon dioxide-amine reaction products. The CDL binders can beself-crosslinking or can be used in admixture with known crosslinkingagents. Examples of such crosslinking agents are aminoplastic resins,crosslinking agents having terminal double bonds, polyepoxy compounds,crosslinking agents having cyclic carbonate groups, crosslinking agentscontaining transesterifiable and/or transamidatable groups, and,especially, blocked polyisocyanates.

In connection with the cleaning agents according to the invention, theterm “EDL binders” means EDL binders as such or EDL binders pluscrosslinking agents for the EDL binders. The cleaning agents accordingto the invention can, therefore, contain EDL binders, for exampleself-crosslinking EDL binders, or EDL binders and crosslinking agents.

It is preferred for the cleaning agents according to the invention tocontain the same EDL binders and, optionally, crosslinking agents as theEDL baths whose ultrafiltration systems are cleaned using the cleaningagents according to the invention.

In addition to water and EDL binders, the aqueous cleaning agentsaccording to the invention contain neutralising agents corresponding toan overneutralisation of the EDL binders, for example corresponding to adegree of neutralisation of the EDL binders of from more than 100 to1000%. Preferred examples of bases used as neutralising agents for ADLbinders are bases conventionally employed in ADL's, such as amines oramino alcohols. Preferred examples of acids used as neutralising agentsfor CDL binders are acids conventionally employed in CDL's, such asorganic monocarboxylic acids, such as, for example, lactic acid, formicacid, acetic acid, or sulfonic acids, such as, for example,amidosulfonic acid, N-alkylamidosulfonic acid, methanesulfonic acid. Itis preferred for the cleaning agents according to the invention tocontain the same neutralising agents as the EDL baths whoseultrafiltration systems are cleaned using the cleaning agents accordingto the invention.

The aqueous cleaning agents according to the invention can containorganic solvents, for example preferably in an order of magnitude as inthe EDL bath, for example of up to 10 wt. %, preferably from 0 to 5 wt.%. Particularly preferably, they contain from 0 to less than 1 wt. %organic solvents. Examples of organic solvents are especiallywater-soluble organic solvents, such as glycol ethers, for example butylglycol, ethoxypropanol; alcohols, such as isopropanol, isobutanol,n-butanol. If the cleaning agents according to the invention containorganic solvents, it is preferred for them to contain the same solventsas the EDL baths whose ultrafiltration systems are cleaned using thecleaning agents according to the invention.

The cleaning agents according to the invention can be prepared by mixingtogether, in the desired relative proportions, EDL binders and,optionally, crosslinking agents, neutralising agents and water as wellas, optionally, organic solvents. Instead of water, it is also possibleto use EDL ultrafiltrate. For example, the cleaning agents according tothe invention can be prepared by mixing together, in the appropriaterelative proportions, an aqueous EDL dispersion containingunderneutralised or completely neutralised EDL binders and, optionally,crosslinking agents, and neutralising agents in an amount sufficient tooverneutralise the EDL binders, water (or EDL ultrafiltrate) and,optionally, organic solvents.

EDL dispersions are aqueous dispersions of EDL binders and, optionally,crosslinking agents for the EDL binders. The EDL binders are present inthe EDL dispersions in a form neutralised with neutralising agent. Theymay be underneutralised or completely neutralised. Completeneutralisation is here not to be confused with 100% neutralisation, butis always less than 100%. Complete neutralisation is present when theafore-described amount of neutralising agent has been used forneutralising the EDL binders, and corresponds, in the case of both ADLbinders and CDL binders, to degrees of neutralisation of, for example,from 40% to, for example, not more than 60%, based on the BDL binder assuch. When complete neutralisation is exceeded, the termoverneutralisation is used. EDL dispersions have solids contents of, forexample, from 30 to 45wt. % and a content of organic solvents ofpreferably less than 5 wt. %, based on the dispersion solids.

EDL dispersions can be prepared by synthesising EDL binders in thepresence or absence of organic solvents and converting the resultingbinders into an aqueous dispersion by dilution with water of the EDLbinders previously neutralised with neutralising agent. The EDLbinder(s) may be present in admixture with one or more suitablecrosslinking agents and can be converted into the aqueous dispersiontogether therewith. Organic solvent, where present, can be removed tothe desired content before or after the conversion into the aqueousdispersion, for example by distillation in vacua. It is possible toavoid the subsequent removal of solvents if, for example, the EDLbinders optionally present in admixture with crosslinking agents areneutralised with neutralising agent in the low-solvent or solvent-freestate, for example in the form of a solvent-free melt at temperaturesof, for example, up to 140° C., and are then converted into the EDLdispersion with water. It is likewise possible, for example, to avoidthe removal of organic solvents if the EDL binders are used initially inthe form of a solution in a radically polymerisable, olefinicallyunsaturated monomer, or the binder synthesis is carried out in aradically polymerisable monomer (e.g. styrene) as solvent, conversioninto an aqueous dispersion is then carried out by neutralisation withneutralising agent and dilution with water, and the radicallypolymerisable monomer is subsequently removed by polymerisation.

The cleaning agents according to the invention can be used for cleaningEDL ultrafiltration membranes. Accordingly, the invention relates alsoto a process for cleaning EDL ultrafiltration membranes using thecleaning agents according to the invention.

The process according to the invention is suitable for the cleaning ofmembranes in EDL ultrafiltration systems, irrespective of the type ofultrafiltration module in question. Examples of different types of EDLultrafiltration modules are plate-type ultrafiltration modules, tubularultrafiltration modules, tube-bundle ultrafiltration modules, as well asspiral wound ultrafiltration modules, which are particularly compact inconstruction.

The process according to the invention is not subject to any limitationsas regards the nature of the ultrafiltration membranes, for example asregards the membrane material and the pore size, but is suitable forcleaning all ultrafiltration membranes conventionally used in BDLultrafiltration units. Examples of membrane materials are polysulfones,polyether sulfones, polyvinylidene fluoride, polyacrylonitrile; the porewidths of the ultrafiltration membranes to be cleaned by the processaccording to the invention are, for example, from 5 to 600 nm.

The cleaning process according to the invention is not subject to anylimitations regarding the composition of the EDL baths ultrafiltered bythe EDL ultrafiltration membranes that are to be cleaned.

The cleaning of EDL ultrafiltration membranes is generally carried outwhenever the ultrafiltration performance, which is expressed as the fluxrate (volume of ultrafiltrate per unit time), declines markedly andfalls below a defined limiting value or a defined fraction of theinitial performance.

For the purposes of cleaning, the EDL ultrafiltration operation isinterrupted, either with the EDL coating process being maintained orwith the EDL coating process being interrupted. It is possible tomaintain the EDL coating process, for example, when the EDLultrafiltration unit has a plurality of ultrafiltration modules and onlyone ultrafiltration module or some of the ultrafiltration modules arecleaned by the process according to the invention, while the remainingultrafiltration modules continue to operate in the intended manner.

If all the ultrafiltration modules are cleaned simultaneously by theprocess according to the invention, the EDL coating process canoptionally be interrupted, for example if an inadequate supply of EDLultrafiltrate is available for bridging the duration of the cleaningoperation. For cleaning, EDL bath material present in the EDLultrafiltration unit is rinsed out with wafer or EDL ultrafiltrate andfed back to the EDL bath. The cleaning agent according to the inventionis then circulated through the EDL ultrafiltration unit.

The throughput of cleaning agent according to the invention is high; forexample, the throughput of cleaning agent according to the inventioncirculated through an ultrafiltration module that is to be cleaned of anEDL ultrafiltration unit operated on an industrial scale may be from 2to 20 m³ per hour. Rinsing with the cleaning agent according to theinvention is carried out, for example, in the same pressure range in(initial pressure at the EDL ultrafiltration module in question) as theultrafiltration of the EDL bath material, preferably in the range frommore than 1 to 2 bar. In general, the cleaning agent according to theinvention is itself separated into a concentrate and an ultrafiltrate,it being preferred for the two components to be added again to thecirculating cleaning agent.

The cleaning agents according to the invention can be used for thecleaning of EDL ultrafiltration membranes either immediately after theirpreparation, by mixing of their constituents, or after a maturing timeof, for example, up to 12 hours has first been allowed to elapse. Thecleaning agent according to the invention can be used for the cleaningof the EDL ultrafiltration membranes at a temperature of, for example,from 20 to 60° C., preferably from 40 to 55° C. The duration of thecleaning operation is, for example, from 5 to 24 hours. The cleaningparameters of cleaning agent throughput, pressure, temperature andduration can be worked out or optimised in each individual case by theperson skilled in the art by means of simple tests.

When the cleaning operation is complete, the cleaning agent can bediscarded or, if its cleaning action is still adequate, can be storedfor further use in subsequent cleaning cycles.

In a preferred embodiment, the process according to the invention iscarried out using an aqueous cleaning agent that contains the same EDLbinder(s) and, optionally, crosslinking agent(s) as well as the sameneutralising agent and, if the aqueous cleaning agent contains organicsolvents, the same organic solvents as the EDL baths whoseultrafiltration systems are cleaned using the cleaning agent accordingto the invention. The cleaning agent then does not have to be discardedonce the cleaning operation is complete, but can be added to the EDLbath in question, which contains the same binders and, optionally,crosslinking agents, the same neutralising agents and—where present—thesame organic solvents. Such a procedure is particularly preferredbecause it does not give rise to any problems with regard to thedisposal of the aqueous cleaning agents after they have been usedaccording to the invention.

The addition of the used aqueous cleaning agent to the EDL bath causesthe neutralising agent content to rise above the afore-mentionedcomplete neutralisation of the EDL binders, since the cleaning agentintroduces overneutralised EDL binder into the EDL bath. In practice,however, that is usually of no or little significance. This becomesevident when the dimensions of industrial EDL coating plants arevisualised. For example, EDL ultrafiltration systems are cleaned by thecirculation of from 50 to 3000 liters of the aqueous cleaning agentaccording to the invention. When the cleaning operation is complete,that amount of used aqueous cleaning agent is added to the EDL bathhaving a volume of, for example, from 30 to 500 m³, so that the increasein the neutralising agent content in the EDL bath is, ultimately,minimal. In the case of smaller baths, the amounts are correspondinglylower. If the increase in the neutralising agent content in the EDL bathcannot or is not to be tolerated, it is possible for the excess amountof neutralising agent in the EDL bath to be compensated for in thecourse of the solids compensation of the EDL bath that is necessary atregular intervals. During the EDL coating process, solids are dischargedfrom the EDL bath as a result of the deposition of ED lacquer on thesubstrate. EDL baths therefore require regular solids compensation,which can be effected, for example, by the addition of correspondingamounts of aqueous EDL dispersion and pigment paste to the EDL bathdepleted of solids. The EDL dispersion can be completely neutralised, orit is underneutralised and the amount of neutralising agent required forcomplete neutralisation is added separately. The afore-mentionedcompensation of the excess neutralising agent in the EDL bath can,therefore, be carried out by using, in the solids compensation of theEDL bath, an appropriate amount of underneutralised EDL dispersionand/or a correspondingly smaller amount of neutralising agent in thecase of the separate addition of neutralising agent.

The cleaning agents according to the invention and the cleaning processaccording to the invention permit effective cleaning of EDLultrafiltration membranes. The cleaning intervals are long and theperformance of the EDL ultrafiltration membranes after cleaning is high.When the cleaning process according to the invention is used, theultrafiltration modules or membranes have a long useful life, since thefall in performance from one cleaning operation to the next described atthe beginning does not occur, or its progression is substantiallyflatter as compared with the cleaning processes of the prior artdescribed at the beginning.

A further advantage of the process according to the invention is thatconditioning (impregnation) of the EDL ultrafiltration membrane does nothave to be carried out after the actual cleaning operation; on thecontrary, the EDL ultrafiltration system can be coupled with the EDLbath contents again and can resume its intended operation immediatelyafter the cleaning operation.

EXAMPLES Example 1 Preparation of a Cleaning Agent for CDLUltrafiltration Membranes, Comparison

A cleaning agent for CDL ultrafiltration membranes is prepared by mixingthe following constituents:

-   -   86 parts by weight of deionised water,    -   4 parts by weight of pure acetic acid,    -   10 parts by weight of butyl glycol

The resulting mixture is warmed to 50° C.

Example 2 Preparation of a Cleaning Agent for CDL UltrafiltrationMembranes, According to the Invention

A 35 wt. % CDL dispersion that has an amine content of 60milliequivalents per 100 g of solids (solids formed by aminoepoxy resinbinder and blocked polyisocyanate crosslinking agent), that contains 1wt. % phenoxypropanol as solvent and that has been neutralised withacetic acid corresponding to a content of 30 milliequivalents of acidper 100 g of solids is mixed with 25 wt. % acetic acid and deionisedwater and thereby adjusted to a solids content of 25 wt. % and a degreeof neutralisation of 240%, and is stirred for 3 hours at 50° C.

Example 3 Cleaning of a CDL Ultrafiltration Module Without Impregnation,Comparison

A CDL ultrafiltration module (spiral wound module) having anultrafiltration membrane area of 16 square meters is cleaned following adrop in performance, occurring as a result of a continual CDLultrafiltration operation, from an initial flux rate of 460 liters ofultrafiltrate per hour to 300 liters of ultrafiltrate per hour. To thatend, the CDL bath material in the ultrafiltration module to be cleanedis first rinsed out with ultrafiltrate. The cleaning agent from Example1 is then circulated through the ultrafiltration module for 14 hours at50° C., an initial pressure at the ultrafiltration module of 3 bar and athroughput of 12 cubic meters per hour. The cleaning agent in theultrafiltration module is subsequently rinsed out with deionised water.Rinsing with CDL ultrafiltrate is then carried out, and theultrafiltration module is then coupled with the CDC bath contents againand normal ultrafiltration operation is resumed. The initial flux rateis 460 liters of ultrafiltrate per hour.

Example 4 Cleaning of a CDL Ultrafiltration Module With Impregnation,Comparison

Example 3 is repeated with the difference that, after rinsing thecleaning agent out of the ultrafiltration module with deionised water,impregnation of the ultrafiltration module is carried out by rinsingwith a 0.5% aqueous solution of Kochkleen™ P3 (Koch, Düsseldorf). Aftersubsequently rinsing with CDL ultrafiltrate, the ultrafiltration moduleis coupled with the CDC bath contents again and normal ultrafiltrationoperation is resumed. The initial flux rate is 460 liters ofultrafiltrate per hour.

Example 5 Cleaning of a CDL Ultrafiltration Module, According to theInvention

Example 3 is repeated with the difference that the cleaning agent fromExample 2 is used instead of the cleaning agent from Example 1. Rinsingout of the cleaning agent after the cleaning operation and separateimpregnation are not carried out. On the contrary, the ultrafiltrationmodule is coupled with the CDC bath contents again and normalultrafiltration operation is resumed. The initial flux rate is 460liters of ultrafiltrate per hour.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows curves showing the fall in the ultrafiltration performancewith time (flux rate in liters of ultrafiltrate per hour, plottedagainst the duration of the ultrafiltration operation in days) of theCDL ultrafiltration module cleaned according to Examples 3, 4 and 5(according to the invention) during the continuous CDL ultrafiltrationoperation resumed following cleaning.

-   -   Example 3: curve with square symbols,    -   Example 4: curve with triangular symbols,    -   Example 5: curve with circular symbols.

The ultrafiltration module cleaned according to Examples 3 and 4 showprogressions that differ only insignificantly from one another.

Starting from a comparable initial level, the progression of the fall inthe ultrafiltration time in the case of the CDL ultrafiltration modulecleaned according to Example 5 is substantially flatter.

1. An aqueous cleaning agent for ultrafiltration membranes inultrafiltration units of electro-dipcoating plants comprising anelectro-dipcoating lacquer binder, wherein the electro-dipcoatinglacquer binder is ovemeutralized with a neutralizing agent correspondingto a degree of neutralization of the binder of at least 100 to 1000%. 2.The aqueous cleaning agent according to claim 1, further comprising upto 10 wt-% of an organic solvent.
 3. The aqueous cleaning agentaccording to claim 2, wherein the organic solvent is a water-solublesolvent.
 4. The aqueous cleaning agent according to claim 3, wherein thewater-soluble solvent is selected from glycol ethers or alcohols.
 5. Theaqueous cleaning agent according to claim 2, further comprising betweenabout 0 and 5 wt-% of the organic solvent.
 6. The aqueous cleaning agentaccording to claim 5, further comprising up to 1 wt-% of an organicsolvent.
 7. The aqueous cleaning agent according to claim 1, wherein theaqueous cleaning agent contains the electro-dipcoating lacquer binder inan amount ranging from 5 to 35 wt-%.
 8. The aqueous cleaning agentaccording to claim 7, wherein the aqueous cleaning agent contains theelectro-dipcoating lacquer binder in an amount ranging from 10 to 30wt-%.
 9. The aqueous cleaning agent according to claim 8, wherein theaqueous cleaning agent contains the electro-dipcoating lacquer binder inan amount ranging from 15 to 28 wt-%.
 10. The aqueous cleaning agentaccording to claim 1, wherein the electro-dipcoating lacquer binder isselected from the group consisting of an anodic dipcoating lacquerbinder and a cathodic electro-dipcoating lacquer binder.
 11. The aqueouscleaning agent according to claim 10, wherein the anodic dipcoatinglacquer binder has an acid number ranging from 35 to 300 mg KOH/g. 12.The aqueous cleaning agent according to claim 11, wherein the anodicdipcoating lacquer binder is selected from the group consisting ofpolyesters, epoxy resin esters, (meth)acrylic copolymer resins, maleateoils and polybutadiene oils.
 13. The aqueous cleaning agent according toclaim 11, wherein the anodic dipcoating lacquer binder isself-crosslinking.
 14. The aqueous cleaning agent according to claim 11,wherein the anodic dipcoating lacquer binder further includes across-linking agent.
 15. The aqueous cleaning agent according to claim10, wherein the cathodic dipcoating lacquer binder has an amine numberranging from 20 to 250 mg KOH/g.
 16. The aqueous cleaning agentaccording to claim 15, wherein the cathodic dipcoating lacquer binder isselected from the group consisting of amino(meth)acrylic resins,aminopolyurethane resins, polybutadiene resins containing amino groups,aminoepoxy resins and epoxy resin-carbon dioxide-amine reactionproducts.
 17. The aqueous cleaning agent according to claim 15 whereinthe cathodic dipcoating lacquer binder is self-crosslinking.
 18. Theaqueous cleaning agent according to claim 15, wherein the cathodicdipcoating lacquer binder and further includes a crosslinking agent. 19.The aqueous cleaning agent according to claim 1, wherein theelectro-dipcoating lacquer binder is an anodically depositable binderand the neutralizing agent is a base.
 20. The aqueous cleaning agentaccording to claim 19, wherein the neutralizing agent is selected fromthe group consisting of amine and amino alcohols.
 21. The aqueouscleaning agent according to claim 1, wherein the electro-dipcoatinglacquer binder is a cathodically depositable binder and the neutralizingagent is an acid.
 22. The aqueous cleaning agent according to claim 21,wherein the neutralizing agent is selected from the group consisting oforganic monocarboxylic acids and sulfonic acids.
 23. A process forcleaning electro-dipcoating ultrafiltration membranes comprising thestep of circulating the aqueous cleaning agent of claim 1 through anultrafiltration module of an electro-dipcoating lacquer ultrafiltrationunit operated on an industrial scale at a throughput ranging from 2 to20 m³ per hour, thereby cleaning the electro-dipcoating ultrafiltrationmembranes.
 24. The process according to claim 23, further comprisingadding the aqueous cleaning agent to an electro-dipcoating bathsubsequent to cleaning, wherein the electro-dipcoating bath comprisesthe same neutralizing agent as in the cleaning agent.
 25. A process forcleaning at least one ultrafiltration membrane comprising rinsing the atleast one ultrafiltration membrane with the aqueous cleaning agentaccording to claim 1.